24 inch 1920x1080 is now the default monitor. No point going smaller. They cost <$200.

Other options include:
- Taking a risk and spending ~$300 on a 2560x1440 27 incher from eBay. Techspot has it on Xmas Shopping List.
- Spending a little more and getting either a 27inch 1080p monitor, or a productivity-oriented 1920x1200 monitor.
- Check out Dell website for more sizes and resolutions. You're gonna be paying for it, though.